The present invention concerns canard equipped aircraft and particularly such aircraft wherein canard lift may be varied.
In canard type aircraft, the small forwardly located wing termed a canard, provides lift forward of the aircarft center of gravity while the main wing center of lift is rearward of the center of gravity. When the canard and wing lift forces are in equilibrium the aircraft is stable, with no movement about its lateral or pitch axis. Currently provision is made in light aircraft of the canard type for altering canard lift for purposes of trimming the aircraft for stable flight, which is typically accomplished by a trim setting of the canard elevators, which incurs increased drag and lowers aircraft performance. Additionally, such trim positioning of canard elevators incurs the risk of "running out of elevator" when large trim adjustments are required, thereby precluding additional elevator movement for steep turns or approach and landing pitch changes.
A drawback to light aircraft of the canard type is that for the most part they do not utilize wing flaps since the trailing edge of the main wing is rearwardly remote from the aircraft center of gravity and would cause severe forward pitching of the aircraft as a conventional, fixed canard cannot counteract such forward pitching. Accordingly, light canard aircraft are usually without flaps and thus require greater landing and take-off distances than other light aircraft of comparable size and weight.
A still further problem with light aircraft of the canard type is that when the same are flown with less than an optimum weiqht distribution in the pilot, passenger and baggage areas, the aircraft must again be trimmed by setting of its elevators with the resulting increased drag and reduced aircraft performance. To resolve this problem, it is often necessary to carry deadweight in a seat or baggage area to keep the aircraft center of gravity within allowable limits. This practice is highly inconvenient and greatly reduces efficiency of operation.
The prior art on aircraft with positionable canards discloses such aircraft are of the military type and for the most part utilize swingable canards for changing canard lift forces. One such patent, U.S. Pat. No. 4,010,920, discloses a canard that is a primary flight control and positionable fore and aft along the longitudinal axis of the aircarft to change the canard moment arm as well as being positionable about said axis. The arrangement disclosed in the patent clearly does not lend itself to utilization in light aircraft by reason of weight, complexity and cost nor is it coupled to main wing flaps.
U.S. Pat. No. 4,569,493 discloses canards rotatable about a horizontal axis transversely disposed to the aircraft longitudinal axis. U.S. Pat. No. 3,778,926 discloses a toy aircraft having a manually settable canard. U.S. Pat. Nos. 3,883,094; 4,161,300 and 4,542,866 disclose canards positionable about multiple axes parallel and perpendicular to the aircraft longitudinal axis. U.S. Pat. Nos. 4,093,156; 2,924,400 and 3,926,389 disclose canards which swing about vertical axes to vary canard sweep and lift. U.S. Pat. No. 2,271,226 discloses a canard type aircraft with canard elevators connected to main wing flaps.